Loudspeaker systems

ABSTRACT

Loudspeaker systems which include a loudspeaker assembly and a thin, slack, easily movable, essentially nonresilient backing member located behind the loudspeaker assembly. The movable member acts to avoid the effects on the cone of the loudspeaker assembly of compression and rarefaction of the air mass behind the assembly caused by rearwardly directed sound waves emanating therefrom, thereby to provide substantially unimpeded movement of the loudspeaker cone of the assembly.

United States Patent l 13,554,313

[72] Inventor Richard Owen Young 2,121,008 6/1938 Bilhuber 181/31 1110 S. Scoville Ave., Oak Park, Ill. 60304 2,713,396 7/1955 Tavares 181/31 [2]] Appl. No. 777,348 2,718,931 9/1955 Boudouris 181/31 [22] Filed Nov. 20, 1968 2,797,766 7/1957 Sullivan 181/31 [45] Patented Jan. 12, 1971 3,302,748 2/1967 Reed 181/31 3,329,236 7/1967 Arden 181/31 [54] LOUDSPEAKER SYSTEMS Primary Examiner-Stephen J. Tomsky Attorney-Wal1enstein, Spangenberg, Hattis and Strampel ABSTRACT: Loudspeaker systems which include a loudspeaker assembly and a thin, slack, easily movable, essentially nonresilient backing member located behind the loudspeaker assembly. The movable member acts to avoid the effects on the cone of the loudspeaker assembly of compression and rarefaction of the air mass behind the assembly caused by rearwardly directed sound waves emanating therefrom, thereby to provide substantially unimpeded movement of the loudspeaker cone of the assembly.

LOUDSPEAKER SYSTEMS This invention relates generally to loudspeakers and enclosures therefor which are capable of high fidelity reproduction of sound.

'I-Ieretofore, loudspeaker enclosures of different sizes, shapes and configurations have been developed in an attempt to provide loudspeake.- svstems which would reproduce sound with a fidelity as nearly as possible to the original sound which was recorded. These different kinds of loudspeaker systems fall into four general categories, infinite baffle, bass-reflex, acoustic suspension, and rubber-backed cabinet types.

The infinite bafile loudspeaker system comprises a large panel or wall onto which a loudspeaker is mounted. To be effective the panel must be large enough so that at the lowest desired frequency the front and rear sound waves travel at least one half wavelength from the loudspeaker to the outer edges of the panel. For example, with a frequency of 20Hz, the distance between the loudspeaker and-the outer edges of the panel would be 28 feet. While infinite baffles of this type give good results in that they prevent cancellation of audible sound waves and permit both the front and rear of the loudspeaker to operate in air at atmospheric pressure, they have certain disadvantages chief among which is the need' for a very large panel to support the loudspeaker thereby making them impractical for use in the average typical home, for example.

In a bass-reflex loudspeaker system, the enclosure or cabinet in which the loudspeaker is mounted is merely a resonator for frequencies below the resonant frequency of the loudspeaker within the cabinet. The bass-reflex system is constructed in a manner to extend the low frequency response range of the loudspeaker, and to prevent cancellation of audible sound waves by inverting thephasewith the forwardly travelling wave. Bass-reflex enclosures can be made smaller to approach bookshelf size but in so doing the efficiency of the loudspeaker system is decreased and the quality of the low frequency sounds is reduced. Also, bass-reflex enclosure cabinets must be tuned for the particular type of loudspeaker used within the cabinet and, therefore,interchangeability of different types of loudspeakers of the same size and cabinets of different configuration is not possible without loss of fidelity of the low frequency sounds.

The acoustic suspension loudspeaker system uses a totally sealed rigid enclosure which can be made small in size. However, with an enclosure volume of less than 9'cubic feet, the compressibility of the air mass within the enclosure begins to act upon the rear surface of the loudspeaker cone, thereby raising the resonant frequency of the loudspeaker system. That is, the low frequency resonant point of the loudspeaker system is increased with decreasing enclosure volume because of increasing effects of compression and rarefaction of the air mass within the enclosure. Therefore, compression of the air mass within the rigid enclosure has an adverse affect on the tonal qualities of the bass notes of music which are produced by the loudspeaker system. Another disadvantage. of such sealed rigid enclosures is that their small size raises the power requirements to drive the loudspeaker sufficiently to produce suitable volume levels. This is caused by the compression and rarefaction of the air mass behind the, loudspeaker which produces forces acting on the loudspeaker opposite to the driving forces induced into the loudspeaker coil. Thus, the efficiency of such loudspeaker systems is greatly reduced, and amplifiers of high power output are required to compensate for this effect. Also, the cost of acoustic suspension loudspeaker systems is greater because of the relatively high cost of loudspeakers of special design which are required for best performance.

The rubber-backed loudspeaker enclosure comprises a box or cabinet, having one or more loudspeakers mounted therein,

increase the efficiency of the system. However, the tightly stretched condition of the sheet, which is further stretched in and out by the outward and inward movements of the cone of the loudspeaker, together with its relatively large mass, combine to place a load on the conesof loudspeakers mounted in the box or cabinet thereby adversely affecting the sound reproduction characteristics of the loudspeaker system.

In accordance with the present invention, loudspeaker systems are provided which substantially eliminate any adverse effects on the sound reproducing movement of a loudspeaker diaphragm or cone resulting from the compression and/or rarefaction of the air mass behind the cone caused by rearwardly moving sound waves emanating from the loudspeaker, while at the same time containing and preventing the sound waves from the rear of the loudspeaker cone from reaching or meeting the sound waves from the front of the loudspeaker cone. The loudspeaker systems of the invention enable high fidelity reproduction of sound to be attained in a smaller sized unit than would otherwise be possible. These results, moreover, are achieved at nominal cost utilizing conventional loudspeaker assemblies. I

Briefly, the loudspeaker systems of this invention involve the use of a thin, slack, lightweight, essentially nonresilient, easily movable backing member located behind a loudspeaker assembly in such a manner as to form an'air chamber which moves in response to rearwardly moving sound waves transthe back wall of which is formed by a tightly stretched sheet of rubber, or other resilient material. The rubber sheet may be stretched to form a resilient planar wall, or it may be stretched partially around one ormore bars-or cleats to form a plurality of surfaces and is intended to reduce the compression and rarefaction of the air mass behind the loudspeaker, thereby to cone 18. The large end of the cone l8 is resiliently mounted to mitted by the assembly and which effectively contains such waves and prevents their escape into the intended listening area. The backing member in one of its forms comprises a partially inflated, substantially air-impervious, baglike enclosure, the periphery of the open endof which is secured in substantially airtight relation to a loudspeaker support frame in the area of the major diameter of the cone of the loudspeaker. The size of the baglike enclosure and the extent to which it is inflated are such that it will not collapse against the rear of the loudspeaker assembly due to rarefaction of the air rr'iasswithi n the enclosure when the loudspeaker cone moves in a forward direction, and will not stretch'tight or become rigid due to compression of the air mass within the enclosure when the loudspeaker cone moves in a'r'earward direction. Loudspeaker assemblies of this invention thusly constructed may be secured to a mounting board which may or may not be the front wall of a loudspeaker cabinet.

In another of its forms, the backing member comprisesa loose, slack, or sagging wall-like body which serves as the rear wall of a loudspeaker cabinet, for example, incorporating one or more loudspeakers. As in the case of the previously described baglike enclosure form of the backing member, the loose wall-like body is secured along its margins insubstantially airtight relation to the top, side and bottom walls of the loudspeaker cabinet, or the like;

These and other features and advantages of the invention" will be more fully appreciated and understood sanita ion" lowing detailed description when taken in conjunction-waif the accompanying drawing wherein-like reference throughout the various views of the drawing are intended to designate similar elements or components.

FIG. 1 is a side elevational sectional view'oforieforiii ofa" loudspeaker system of this invention;

FIG. 2 is a rear view of the system of FIG. 1;

FIG. 3 is a side elevational sectional view of anothe rftir'rii df a loudspeaker system of thisinvention; FIG. 4 is a sectional view taken along line 4-4 of FIG. 3',

FIG. 5 is a perspective view of a modified form-bf'tiie lodd I speaker system shown inFIGS. Sand 4; and FIG. 6 is a sectional view taken along line 6-6 of FIG. 5. Referring now, to FIGS. 1 and 2 of the drawing, thelbbd speaker system of the present invention there illustrated conrprises a loudspeaker assembly 10 and a flexible, partiallyin'} flated, baglike enclosure 12. The assembly 10 maybe of con;

ventional construction and design,-and includes'a 's uppoit frame 14, a magnet and coil element 16 and a loudspeaker the annular portion 14a of the support frame 14 in such a manner as to facilitate controllable forward and rearward movement of the cone 18 under the influence of the magnet and coil element 16. The assembly desirably is located and mounted over an aperture 20 which is formed through a mounting board 22, a d may be secured to the board 22 by an suitable means such as bolts or screws. A grill cloth 24 overlies the aperture 20.

A pair of electrical leads 26-26 are connected to the magnet and coil element 16 and extend through openings conveniently located within the annular portion 14a of the support frame 14 for connection to a suitable source of audio frequency electrical signals.

As illustrated, the baglike enclosure 12 completely encases the rear portion of the assembly 10, and is secured, in substantially airtight relation, along its free margin 28, to the annular portion 14a of the support frame 14. The enclosure 12 may be fabricated of any thin, lightweight, substantially air-impervious, flexible sheet material. In accordance with the preferred embodiment of the invention, the enclosure 12 is formed of a plastic sheet material such as polyethylene, polypropylene, cellophane and the like. Any means known in the art may be used to attain a suitable seal between the margin 28 of the enclosure 12 and the annular portion 14a of the support frame 14. The enclosure 12, as indicated here'inabove, is of a size, and is inflated to an extent, whereby it will not collapse against, or make contact with the rear of the loudspeaker assembly 10 when the cone 18 of the assembly is driven to its full forward position and will not become tightly stretched when the cone 18 is driven to its full rearward position.

In operation, rapid forward and rearward movement of the loudspeaker cone 18, as a result of its being driven by an audio amplifier, will cause slight increases and decreases in the air pressure in the chamber defined by the enclosure 12. The thin, slack, lightweight, flexible character of the baglike enclosure 12 enables it to easily move in response to these slight increases and decreases in air pressure, and to effectively prevent any adverse effects they may have on the sound producing movement of the cone 18. Thus, the loudspeaker assembly is able to operate freely and with a high degree of efficiency, while at the same time, the sound waves from the rear of the loudspeaker cone are contained and prevented from reaching or meeting the sound waves from the front of the loudspeaker cone.

In the embodiment of the invention illustrated in FIGS. 3 and 4 of the drawing, the loudspeaker system comprises a wooden cabinet 30 adapted to house one or more loudspeaker assemblies such as the assembly 32. The cabinet 30 includes a front wall or panel 34 on which the assembly 32 is mounted, a

top wall 36, a bottom wall 38 and sidewalls 40-40. The rear wall is formed by a loose, slack, sheetlike body 42 which is secured in substantially airtight relation along its free margins to the top, bottom and sidewalls of the cabinet 30. An airtight seal may be attained in any manner known in the art. Various adhesives, for example, can be used for this purpose. The sheetlike body 42, as in the case of the baglike enclosure 12 of the embodiment of the invention described above, may be made of any thin, lightweight, substantially air-impervious sheet material. Plastic sheet materials such as polyethylene, polypropylene, cellophane, and the like, are preferred. The loudspeaker assembly 32 may be of conventional design and construction, and includes a magnet and coil element 44 and a loudspeaker cone 46. A pair of leads 48-48, for connection to a source of audio frequency electrical signals, are provided.

In FIGS. 5 and 6 of the drawing, a modification of the embodiment of the invention illustrated in H05. 3 and 4 is shown. The loudspeaker system is of the bookshelf type. and includes a wooden cabinet or box 50 in which is mounted a loudspeaker assembly 52. The assembly 52, as before, is of conventional design and construction, and includes a magnet and coil element 54 and a cone 56. The box 50 has a front wall or panel 58 in which the assembly 52 is secured, a top wall 60,

a bottom wall 62 and sidewalls 64-64. The rear wall, as in the embodiment of the invention illustrated in FIGS. 3 and 4, is

formed of a loose, slack, sheetlike body 66, desirably fabricated of plastic sheet material, which is secured in substantially airtight relation along its margins to the top, bottom and sidewalls of the box 52.

In the embodiments of the invention shown in FIGS. 3 through 6, the loose, slack, sheetlike bodies 42 and 66 act to contain and dissipate the effects of the rearward travelling sound waves emanating from the loudspeaker assemblies so that compression and rarefaction of the air mass behind the assemblies will not restrict or impede the free movement of the loudspeaker cone. This enables the assemblies to operate at high efficiency and to achieve high fidelity reproduction of sound.

While for purposes of illustration preferred forms of the present invention have been disclosed, other forms thereof may become apparent to those skilled in the art upon reference to this disclosure, and, therefore, this invention is to be limited only by the scope of the appended claims.

lclaim:

1. A loudspeaker system comprising: a loudspeaker secured to a mounting board and connectable to a source of audio frequency electrical signals, said loudspeaker including a movable loudspeaker diaphragm having an exposed front face for producing sound waves to be transmitted into a listening area and a back face, said diaphragm being controllably energizable in response to audio frequency electrical signals from said source, and a partly inflated, thin, slack, lightweight, easily movable, substantially air-impervious plastic baglike member which completely encases the back face only of the movable loudspeaker diaphragm and serves to form a closed air chamber behind the back face only of the loudspeaker diaphragm, thus being free to produce sound waves for transmission to a listening area, said plastic baglike member having a size and being partly inflated to an extent such that it will not collapse against the back face of the loudspeaker due to movement of the air in said closed chamber when the loudspeaker diaphragm moves in a forward direction and will not stretch tight or become rigid due to compression of the air in said closed chamber when the loudspeaker diaphragm moves in a rearward direction thereby to substantially prevent compression or rarefaction of the air in the closed chamber which would tend adversely to affect the sound wave producing movement of the front face of the loudspeaker diaphragm.

2. A loudspeaker system according ta claim 1 wherein the plastic baglike member has an open end, the periphery of which is secured in substantially airtight relation to the support frame of the loudspeaker in the area of the major diameter of the movable diaphragm of the loudspeaker. 

1. A loudspeaker system comprising: a loudspeaker secured to a mounting board and connectable to a source of audio frequency electrical signals, said loudspeaker including a movable loudspeaker diaphragm having an exposed front face for producing sound waves to be transmitted into a listening area and a back face, said diaphragm being controllably energizable in response to audio frequency electrical signals from said source, and a partly inflated, thin, slack, lightweight, easily movable, substantially air-impervious plastic baglike member which completely encases the back face only of the movable loudspeaker diaphragm and serves to form a closed air chamber behind the back face only of the loudspeaker diaphragm, thus being free to produce sound waves for transmission to a listening area, said plastic baglike member having a size and being partly inflated to an extent such that it will not collapse against the back fAce of the loudspeaker due to movement of the air in said closed chamber when the loudspeaker diaphragm moves in a forward direction and will not stretch tight or become rigid due to compression of the air in said closed chamber when the loudspeaker diaphragm moves in a rearward direction thereby to substantially prevent compression or rarefaction of the air in the closed chamber which would tend adversely to affect the sound wave producing movement of the front face of the loudspeaker diaphragm.
 2. A loudspeaker system according to claim 1 wherein the plastic baglike member has an open end, the periphery of which is secured in substantially airtight relation to the support frame of the loudspeaker in the area of the major diameter of the movable diaphragm of the loudspeaker. 